Pergamon Tetrahedron Letters 39 (1998) 3555-3558 TETRAHEDRON LETTERS Aldoi Condensations Catalysed by Novel Mg-Al-O-t-Bu Hydrotalcite B.M. Choudar~*', M. Lakshmi Kantam °, B. Kavita', Ch. Venkat Reddy', K.Koteswara Rao" and F. Figueras b "Indian Institute of Chemical Technology, Hyderabad- 500007, India b Institut dc Recherehes mr la Catalyse, 2, Avenue Albert Einstein 69626 Villeurbanne cedex - France Received 12 January 1998; revised 5 March 1998; accepted 6 March 1998 Abstract: A novel Mg-AI-O-t-Bu hydrotalcite prepared for the first time, catalyses condensation reactions selectively to aldols (3) at 0°C in quantitative yields. © 1998 ElsevierS :ience Ltd. All rights reserved. There has bq~en increasing attention on the design and use of environmentally compatible solid acid-base catalysts targeted to minimise the emission of effluents in chemical industries. These solid acid-base catalysts can be easily separated and recycled. Layered double hydroxides (LDHs) or hydrotalcite like compounds (HTLCs) have recently received considerable commercial interest ~ as adsorbents, anion exchangers and most important as base catalysts 2"4. Hydrotalcites are represented by the formula [M2÷(1-x)M~÷ x(OHh] x÷(A ~- x/m).nH20, where the M 2+ are the divalent ions and M 3+ are the trivalent ions. The compensating anions may be Off, CI', NOr, COl etc. and on their expulsion at 450°C, LDHs gives a highly active homogeneous mixed oxide which is potentially a basic catalyst for a variety of organic transformations such as aldol condensation s, olefin isomerization2, epoxidations of activated olefins with hydrogen peroxide 6, alkylations of diketones 7, nucleophilic halide exchange s and Clalsen-Schmidt condensation 9 etc. The aldol condensation is of prime importance for fine chemical synthesis and is generally catalysed b) acids or bases t°, In the laboratory, many catalysts have been reported such as alumirtan'~2, zeolites 13, sepiolite ~4, and hydrotalcites 9"is. The reported works ~'7'm~6 on aldolisations were performed at relatively high temperatures. Earlier, we designed and developod modified hydrotalcite by incorporation of hydroxyls during the rehydration process aud found it to be excellent for aldol condensation ~7. Now, we opted a novel approach of in.:orporation of tert-butoxide by an exchange process, to tune up the hydrotalcite for higher basicity. We report in this letter the preparation of Mg-AI-O-t-Bu hydrotalcite and selective condensations to aldol products 0040-4039/98/$19.00 © 1998 Elsevier Science Ltd. All rights reserved. PII: S0040-4039(98)00547-4